|Dear Diary discusses the brake system fitted to Jensen FF chassis number 119/191
From the Jensen FF Mk1 sales literature: “Hydraulically operated self-adjusting Dunlop disk brakes on all 4 wheels. Separate systems for front and rear brakes with booster assisted tandem master cylinder and incorporating Dunlop Maxaret anti-skid device. Swept area 498.2 sq.ins. (32.4 cm2). Central handlever operates self adusting parking brake on rear wheels.”
NB. On my 1969 Mk1 FF, however, the brake system includes Girling disk brakes.
Above, photos of the reconditioned calliper’s both on and off the vehicle. The brake pipes on the rear callipers are actually replaced by copper pipes with brass unions as part of the reconditioning. They were done by Classicar Automotive of Unit A, Alderley Road, Chelford,Cheshire, SK11 9AP. (They advertise in the JOC magazine and were also recommended by several people from the list- they certainly knew about FF’s/Interceptors when I spoke to them.)Front Callipers were £50.00 each + vat; Rear Callipers were £150.00 each + vat;. Postage in England £10.00 The handbrake pads were fitted by the reconditioners as part of the reconditioning and were standard replacement pads. For the front and rear brakes I opted for EBC Kevlar “Green Stuff” disc pads for improved braking performance. . These EBC pads are not needed for the handbrake They are high friction roadsport compound for fast road use and have a higher friction coefficient than ordinary pads. They are effective up to 550 degrees Centigrade and do not produce much dust. The dust produced is non damaging ( better for alloy wheels) and should not exhibit any squealing.. Note they can be fitted to the front or front and rear but should not be fitted to the rear brakes alone EBC can be contacted for technical info. At EBC Buildings, Countesse Rd Northampton NN5 7EA tel 01604 583344Cost- Front Pad Set (Part No. DP 2108)-£40.00 + vat; Rear Pad Set (Part No. 2101)-£32.00 + vat; Handbrake pads £28.00 + vat;(Total cost including postage both ways and vat -£608.09p)
The brake pipes have now been replaced with Kunifer (copper/nickel) brake piping, with brass 3/8th UNF threaded ends (the ends were obtained from Automec Equipment and parts Ltd. 36 Ballmoor, Buckingham, Buckinghamshire, England MK18 1RQ. Tel 01280 822818 (www.automec.co.uk.). They will also fabricate the pipes in either Kunifer or copper.). The copper/nickel alloy is harder than copper and has the same diam. as the old brake pipes and is non rusting.
Photo 1 showing brake hoses. Photo 2 showing the lilac coloured silicon dot 5 brake fluid in the reservoirs. The original brake hoses are to be replaced with Goodrich stainless steel braided hoses I’m also using silicon brake fluid to avoid seizing in the future and the need to keep changing the fluid. Purchased from Automec Equipment at the NEC Classic Car Show for £20 per litre. One litre would have been enough but after brake bleeding problems I was glad I’d bought 2 litres.. The braided hoses will help make up for the increased compressibility of the silicon fluid and make the pedal feel firmer.These were bought from Flexolite, Brokehill Farm, Mathon Road, Colwall, Herefordshire, WR13 6EP Tel 01684 541941.Total cost £37.50p +vat + £3.50p postage ( Total £48.18p) for the three hoses. I sent them the original hoses as patterns and requested their return.
Note see article below which would appear to be a persuasive counter arguement to using Silicon Brake Fluid. If I race my car I might change my use of Silicin brake fluid. I have used it in my old triumph Vitesse which was set up for Historic Ralleying as well as the Jensen. I have used it for some 15 years now and have never sufferd from seized brakes. Given the intermittent use of our cars this alone persuades me to stick with it. One last point ou shouldn’t just change over to silicon because the old seals in the system will have swollen through absorbtion of the old brake fluid and may leak (so I am told) Only use it in refurbished brake systems incorrporating new seals.
Photos 1& 2 shows the brake master cylinder.and the unit stripped ready for the new seals. Note the black tie that has on it the following notation “66283 0 60/40 44DM” the small right angle cylinder on top has the part number “64676708” written on it. Photo 3 shows its location on the servo I had to replace all the rubbers using kit no. …………..price………………..bought from Cropredy Bridge After replacing all the callipers and bleeding the system, (according to the manual you bleed the nearside front and back together and then the offside front and back, without the engine running and therefor without any vacuum assistance. To achieve this on the nearside the front wheels were put on full right hand lock to enable access to the bleed nipple on the front calliper and the rear jacked up and the wheel removed to allow access to the rear bleed nipple.Both nipples were opened and the brakes on that side bled. (then all change to do the offside.) It still wouldn’t pressurise, the brake pedal would harden up but then slowly go to the floor. At this point I came to the conclusion that the master cylinder needed rebuilding, which I did. Out of interest I have an “Easybleed” brake bleeding kit which I tried to use on the FF, but because of the large diameter Girling brake reservoir caps a suitable sealing cap for the system is not available. I dismantled one of the caps. To my surprise the rivets in the top attaching the black caps were easy to unscrew using a pair of pliers to grip the domed heads. This allowed access to the electrical contacts and the removal of that unit. The cap was now left with a large centre hole. Using two metal washers and one rubber one I was able to attach the Easybleed system to the reservoirs one at a time. Using this the braks were soon fully functional.(According to the Original service documents the brake reservoir was actually replaced under warranty at 2126 miles due to a leak ( part no. CT. 985 )),
I had a problem with the vaccum reseviors depressurising due to an air leak in the left hand tube. I resolved this by simply bypassing the left hand tube and I now only use the right hand tube as a resevior..
ARTICLE RE SILICON BRAKE FLUID | BRAKE SYSTEMS
FROM THE JENSEN OWNERS CLUB TECHNICAL ARCHIVES REGARDING BRAKE SYSTEMS
RETRO- TECH 1
In the July / August issue I had a letter published updating a previous article on water pumps, I also suggested that past features should be reviewed. This has prompted me to write a series of articles reminding (or in some cases reading for the first time) members of technical tips and recommendations from old magazines. I will also add some of the problems, and I hope solutions, given to me as one of the ‘technical advisors’. Overhearing conversations at the last ‘International Weekend’ I am prompted to make the following the first article as it is still current: –
In the November ’93 letters Terry Lawson of Australia told us of the experience of a friend who put silicon brake fluid in his race car but found he repeatedly lost braking efficiency during races. Terry, being a chemist, did some research into this and found that the particular silicon fluids that form the basis of the brake fluid composition are compressible (to a relative large degree in comparison to other liquids). So much so that these fluids were proposed to be used in shock absorbers in aircraft landing gear. I had a similar experience to Terry’s friend during some ‘parade’ laps at Silverstone, after some very vigorous braking I nearly went into the back of Phil Dawson’s Healey. Needless to say I was using silicone.
A few issues later John Pilling wrote this: – I changed the fluid in my FF 11 to silicone. I have never been completely happy with my car as it had a long spongy travel, and once, after much braking on a hot day, the brakes became nearly non-existent. I enquired about my braking difficulties to a brake specialist and he gave me the following service bulletin by ‘AP Lockheed’: –
‘Our technical service department is receiving an alarming number of calls from motorists reporting problems with silicon brake fluids. AP Lockheed neither markets nor recommends their use with our own or any other braking system. Virtually all of the problems relate to: Long, spongy pedal, sudden loss of brakes, hanging on of brakes. They reflect certain properties of silicone fluids identified with us over many years and recently ratified in SAE publications, namely: 1) High ambient viscosity. 2) High air absorption. 3) High compressibility. 4) Low lubricity. 5) Immiscibility with water.
Research has shown that the relationships between problems reported and problems identified may be expressed as follows:
Long and spongy pedal: a) Compressibility – up to three times that of glycol-based fluids. b) High viscosity – twice that of glycol-based fluids, leading to slow rates of
fill and retention of free air entrapped during filling, and hence bleeding difficulties.
Sudden loss of brakes: a) Air absorption. Gasification of absorbed air at relatively low temperature produces vapour-lock effect. B) Immiscibility (failure to mix) with water. Whilst the presence of dissolved water will reduce the boiling point of glycol-based fluids, any free water entrapped in silicone-filled systems will boil and produce vapour lock at much lower temperatures (100 ° C or thereabouts).
Hanging on of brakes: a) Low lubricity. In disc brake systems the sole mechanism for normalisation of system pressure upon release of pedal pressure is a designed-in tendency of seals to recover their ‘at rest’ attitude. Low lubricity works against this tendency. b) High viscosity, exacerbating the effect of a) above.
It should not be assumed therefore, that the high price of silicone fluids implies higher performance in hard driving or even normal road use.’
This prompts the question ‘why do people change to silicon brake fluid?’ The main reasons are that it is non-flammable, it will not discolour or take off your paint-work if leaked or spilt and it will not take in moisture. The first two reasons are very real. The most common cause of under-bonnet fires is from brake fluid being spilt directly onto the exhaust from reservoirs that have not had their tops put on correctly. The remedy is always be careful and cure any leaks especially around the master cylinder area. As for the paint stripping properties of glycol fluid, again be careful when filling and bleeding. The non-absorption of water claimed by silicon fluid manufacturers may be true but as we have read, water will still get in the system. To reduce the effects of this with both fluids is for regular changes of fluid.
I hope the above shows the disadvantages of silicon, I know members are still using it. The good news is that to change from silicon to glycol does not need a complete strip down and seal change only a flush through (the seals do not absorb the silicon), unlike going from glycol to silicon. Also the higher ‘Dot’ numbered glycol fluids now available are proving to be better than anything available before.